Dibenzothiophene-containing materials in phosphorescent light emitting diodes

ABSTRACT

A new class of dibenzothiophene and/or dibenzofuran-containing compounds are provided. The new compounds may be useful in organic light emitting devices, particularly as the host of an emissive layer having a host and an emissive dopant, or as a material in an enhancement layer.

This application claims priority to U.S. Provisional Application Ser. No. 61/017,480, filed Dec. 28, 2007, the disclosure of which is herein expressely incorporated by reference in its entirety. This application is also related to International Application No. PCT/IB2007/004687, filed Dec. 28, 2007.

The claimed invention was made by, on behalf of, and/or in connection with one or more of the following parties to a joint university corporation research agreement: Regents of the University of Michigan, Princeton University, The University of Southern California, and the Universal Display Corporation. The agreement was in effect on and before the date the claimed invention was made, and the claimed invention was made as a result of activities undertaken within the scope of the agreement.

FIELD OF THE INVENTION

The present invention is directed to organic light emitting devices (OLEDs). More specifically, the present invention relates to phosphorescent light emitting materials and devices that may have improved device lifetime.

BACKGROUND

Opto-electronic devices that make use of organic materials are becoming increasingly desirable for a number of reasons. Many of the materials used to make such devices are relatively inexpensive, so organic opto-electronic devices have the potential for cost advantages over inorganic devices. In addition, the inherent properties of organic materials, such as their flexibility, may make them well suited for particular applications such as fabrication on a flexible substrate. Examples of organic opto-electronic devices include organic light emitting devices (OLEDs), organic phototransistors, organic photovoltaic cells, and organic photodetectors. For OLEDs, the organic materials may have performance advantages over conventional materials. For example, the wavelength at which an organic emissive layer emits light may generally be readily tuned with appropriate dopants.

OLEDs make use of thin organic films that emit light when voltage is applied across the device. OLEDs are becoming an increasingly interesting technology for use in applications such as flat panel displays, illumination, and backlighting. Several OLED materials and configurations are described in U.S. Pat. Nos. 5,844,363, 6,303,238, and 5,707,745, which are incorporated herein by reference in their entirety.

One application for phosphorescent emissive molecules is a full color display. Industry standards for such a display call for pixels adapted to emit particular colors, referred to as “saturated” colors. In particular, these standards call for saturated red, green, and blue pixels. Color may be measured using CIE coordinates, which are well known to the art.

One example of a green emissive molecule is tris(2-phenylpyridine)iridium, denoted Ir(ppy)₃, which has the structure of Formula I:

In this, and later figures herein, we depict the dative bond from nitrogen to metal (here, Ir) as a straight line.

As used herein, the term “organic” includes polymeric materials as well as small molecule organic materials that may be used to fabricate organic opto-electronic devices. “Small molecule” refers to any organic material that is not a polymer, and “small molecules” may actually be quite large. Small molecules may include repeat units in some circumstances. For example, using a long chain alkyl group as a substituent does not remove a molecule from the “small molecule” class. Small molecules may also be incorporated into polymers, for example as a pendent group on a polymer backbone or as a part of the backbone. Small molecules may also serve as the core moiety of a dendrimer, which consists of a series of chemical shells built on the core moiety. The core moiety of a dendrimer may be a fluorescent or phosphorescent small molecule emitter. A dendrimer may be a “small molecule,” and it is believed that all dendrimers currently used in the field of OLEDs are small molecules.

As used herein, “top” means furthest away from the substrate, while “bottom” means closest to the substrate. Where a first layer is described as “disposed over” a second layer, the first layer is disposed further away from substrate. There may be other layers between the first and second layer, unless it is specified that the first layer is “in contact with” the second layer. For example, a cathode may be described as “disposed over” an anode, even though there are various organic layers in between.

As used herein, “solution processible” means capable of being dissolved, dispersed, or transported in and/or deposited from a liquid medium, either in solution or suspension form.

A ligand may be referred to as “photoactive” when it is believed that the ligand directly contributes to the photoactive properties of an emissive material. A ligand may be referred to as “ancillary” when it is believed that the ligand does not contribute to the photoactive properties of an emissive material, although an ancillary ligand may alter the properties of a photoactive ligand.

As used herein, and as would be generally understood by one skilled in the art, a first “Highest Occupied Molecular Orbital” (HOMO) or “Lowest Unoccupied Molecular Orbital” (LUMO) energy level is “greater than” or “higher than” a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy relative to a vacuum level, a higher HOMO energy level corresponds to an IP having a smaller absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (EA) having a smaller absolute value (an EA that is less negative). On a conventional energy level diagram, with the vacuum level at the top, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A “higher” HOMO or LUMO energy level appears closer to the top of such a diagram than a “lower” HOMO or LUMO energy level.

As used herein, and as would be generally understood by one skilled in the art, a first work function is “greater than” or “higher than” a second work function if the first work function has a higher absolute value. Because work functions are generally measured as negative numbers relative to vacuum level, this means that a “higher” work function is more negative. On a conventional energy level diagram, with the vacuum level at the top, a “higher” work function is illustrated as further away from the vacuum level in the downward direction. Thus, the definitions of HOMO and LUMO energy levels follow a different convention than work functions.

More details on OLEDs, and the definitions described above, can be found in U.S. Pat. No. 7,279,704, which is incorporated herein by reference in its entirety.

SUMMARY OF THE INVENTION

A new type of materials is provided. The new class of materials has a dibenzothiophene-containing compound selected from the group consisting of:

where each of R₁ through R₆ are independently selected from the group consisting of any aryl and alkyl substituents and H, and where each of R₁ through R₆ may represent multiple substitutions. In one aspect, all of R₁ through R₆ are H.

An organic light emitting device is also provided. The device has an anode, a cathode, an and an organic layer disposed between the anode and the cathode. The organic layer further comprises a material containing a compound from the group consisting of Compound 1G through 12G, as described above, with or without substituents. Preferably the organic layer is an emissive layer having a host and an emissive dopant, and the compound is the host. The compound may also preferably be used as a material in an enhancement layer.

New materials are provided. The materials have a dibenzothiophene-containing and/or dibenzofuran-containing compound selected from the group consisting of:

where each of R₁ through R₈ are independently selected from the group consisting of any aryl and alkyl substituents and H, and where each of R₁ through R₈ may represent multiple substitutions. In one aspect, all of R₁ through R₈ are H.

An organic light emitting device is also provided. The device has an anode, a cathode, and an organic layer disposed between the anode and the cathode. The organic layer further comprises a material containing a compound from the group consisting of Compound 2G through 35G, as described above, with or without substituents. Preferably the organic layer is an emissive layer having a host and an emissive dopant, and the compound is the host. The compound may also preferably be used as a material in an enhancement layer.

A consumer product is also provided. The product contains a device that has an anode, a cathode, and an organic layer disposed between the anode and the cathode, where the organic layer further comprises a material containing a compound from the group consisting of Compounds 2G through 35G, as described above, with or without substituents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an organic light emitting device.

FIG. 2 shows an inverted organic light emitting device that does not have a separate electron transport layer.

FIG. 3 shows an organic light emitting device including compounds disclosed herein.

FIG. 4 shows a plot of normalized luminescence versus time for the device of FIG. 3.

FIG. 5 shows a plot of external quantum efficiency versus luminance for the device of FIG. 3.

FIG. 6 shows a plot of power efficacy versus luminance for the device of FIG. 3.

FIG. 7 shows a plot of luminance versus voltage for the device of FIG. 3.

FIG. 8 shows a plot of EL intensity versus wavelength for the device of FIG. 3.

FIG. 9 shows an organic light emitting device including compounds disclosed herein.

FIG. 10 shows a plot of external quantum efficiency versus luminance for the device of FIG. 9.

FIG. 11 shows a plot of power efficacy versus luminance for the device of FIG. 9.

FIG. 12 shows a plot of luminance versus voltage for the device of FIG. 9.

FIG. 13 shows a plot of EL intensity versus wavelength for the device of FIG. 9.

FIG. 14 shows a dibenzothiophene-containing compound.

DETAILED DESCRIPTION

Generally, an OLED comprises at least one organic layer disposed between and electrically connected to an anode and a cathode. When a current is applied, the anode injects holes and the cathode injects electrons into the organic layer(s). The injected holes and electrons each migrate toward the oppositely charged electrode. When an electron and hole localize on the same molecule, an “exciton,” which is a localized electron-hole pair having an excited energy state, is formed. Light is emitted when the exciton relaxes via a photoemissive mechanism. In some cases, the exciton may be localized on an excimer or an exciplex. Non-radiative mechanisms, such as thermal relaxation, may also occur, but are generally considered undesirable.

The initial OLEDs used emissive molecules that emitted light from their singlet states (“fluorescence”) as disclosed, for example, in U.S. Pat. No. 4,769,292, which is incorporated by reference in its entirety. Fluorescent emission generally occurs in a time frame of less than 10 nanoseconds.

More recently, OLEDs having emissive materials that emit light from triplet states (“phosphorescence”) have been demonstrated. Baldo et al., “Highly Efficient Phosphorescent Emission from Organic Electroluminescent Devices,” Nature, vol. 395, 151-154, 1998; (“Baldo-I”) and Baldo et al., “Very high-efficiency green organic light-emitting devices based on electrophosphorescence,” Appl. Phys. Lett., vol. 75, No. 3, 4-6 (1999) (“Baldo-II”), which are incorporated by reference in their entireties. Phosphorescence is described in more detail in U.S. Pat. No. 7,279,704 at cols. 5-6, which are incorporated by reference.

FIG. 1 shows an organic light emitting device 100. The figures are not necessarily drawn to scale. Device 100 may include a substrate 110, an anode 115, a hole injection layer 120 (HIL), a hole transport layer 125 (HTL), an electron blocking layer 130, an emissive layer 135, a hole blocking layer 140, an electron transport layer 145, an electron injection layer 150, a protective layer 155, and a cathode 160. Cathode 160 is a compound cathode having a first conductive layer 162 and a second conductive layer 164. Device 100 may be fabricated by depositing the layers described, in order. The properties and functions of these various layers, as well as example materials, are described in more detail in U.S. Pat. No. 7,279,704 at cols. 6- 10, which are incorporated by reference.

More examples for each of these layers are available. For example, a flexible and transparent substrate-anode combination is disclosed in U.S. Pat. No. 5,844,363, which is incorporated by reference in its entirety. An example of a p-doped hole transport layer is m-MTDATA doped with F.sub.4-TCNQ at a molar ratio of 50:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. Examples of emissive and host materials are disclosed in U.S. Pat. No. 6,303,238 to Thompson et al., which is incorporated by reference in its entirety. An example of an n-doped electron transport layer is BPhen doped with Li at a molar ratio of 1:1, as disclosed in U.S. Patent Application Publication No. 2003/0230980, which is incorporated by reference in its entirety. U.S. Pat. Nos. 5,703,436 and 5,707,745, which are incorporated by reference in their entireties, disclose examples of cathodes including compound cathodes having a thin layer of metal such as Mg:Ag with an overlying transparent, electrically-conductive, sputter-deposited ITO layer. The theory and use of blocking layers is described in more detail in U.S. Pat. No. 6,097,147 and U.S. Patent Application Publication No. 2003/0230980, which are incorporated by reference in their entireties. Examples of injection layers are provided in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. A description of protective layers may be found in U.S. Patent Application Publication No. 2004/0174116, which is incorporated by reference in its entirety. An “enhancement layer” occupies the same position in a device as a blocking layer described above, and may have blocking functionality or other functionality that improves device performance.

FIG. 2 shows an inverted OLED 200. The device includes a substrate 210, a cathode 215, an emissive layer 220, a hole transport layer 225, and an anode 230. Device 200 may be fabricated by depositing the layers described, in order. Because the most common OLED configuration has a cathode disposed over the anode, and device 200 has cathode 215 disposed under anode 230, device 200 may be referred to as an “inverted” OLED. Materials similar to those described with respect to device 100 may be used in the corresponding layers of device 200. FIG. 2 provides one example of how some layers may be omitted from the structure of device 100.

The simple layered structure illustrated in FIGS. 1 and 2 is provided by way of non-limiting example, and it is understood that embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Functional OLEDs may be achieved by combining the various layers described in different ways, or layers may be omitted entirely, based on design, performance, and cost factors. Other layers not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples provided herein describe various layers as comprising a single material, it is understood that combinations of materials, such as a mixture of host and dopant, or more generally a mixture, may be used. Also, the layers may have various sublayers. The names given to the various layers herein are not intended to be strictly limiting. For example, in device 200, hole transport layer 225 transports holes and injects holes into emissive layer 220, and may be described as a hole transport layer or a hole injection layer. In one embodiment, an OLED may be described as having an “organic layer” disposed between a cathode and an anode. This organic layer may comprise a single layer, or may further comprise multiple layers of different organic materials as described, for example, with respect to FIGS. 1 and 2.

Structures and materials not specifically described may also be used, such as OLEDs comprised of polymeric materials (PLEDs) such as disclosed in U.S. Pat. No. 5,247,190 to Friend et al., which is incorporated by reference in its entirety. By way of further example, OLEDs having a single organic layer may be used. OLEDs may be stacked, for example as described in U.S. Pat. No. 5,707,745 to Forrest et al, which is incorporated by reference in its entirety. The OLED structure may deviate from the simple layered structure illustrated in FIGS. 1 and 2. For example, the substrate may include an angled reflective surface to improve out-coupling, such as a mesa structure as described in U.S. Pat. No. 6,091,195 to Forrest et al., and/or a pit structure as described in U.S. Pat. No. 5,834,893 to Bulovic et al., which are incorporated by reference in their entireties.

Unless otherwise specified, any of the layers of the various embodiments may be deposited by any suitable method. For the organic layers, preferred methods include thermal evaporation, inkjet, such as described in U.S. Pat. Nos. 6,013,982 and 6,087,196, which are incorporated by reference in their entireties, organic vapor phase deposition (OVPD), such as described in U.S. Pat. No. 6,337,102 to Forrest et al., which is incorporated by reference in its entirety, and deposition by organic vapor jet printing (OVJP), such as described in U.S. patent application Ser. No. 10/233,470, which is incorporated by reference in its entirety. Other suitable deposition methods include spin coating and other solution based processes. Solution based processes are preferably carried out in nitrogen or an inert atmosphere. For the other layers, preferred methods include thermal evaporation. Preferred patterning methods include deposition through a mask, cold welding such as described in U.S. Pat. Nos. 6,294,398 and 6,468,819, which are incorporated by reference in their entireties, and patterning associated with some of the deposition methods such as ink-jet and OVJD. Other methods may also be used. The materials to be deposited may be modified to make them compatible with a particular deposition method. For example, substituents such as alkyl and aryl groups, branched or unbranched, and preferably containing at least 3 carbons, may be used in small molecules to enhance their ability to undergo solution processing. Substituents having 20 carbons or more may be used, and 3-20 carbons is a preferred range. Materials with asymmetric structures may have better solution processibility than those having symmetric structures, because asymmetric materials may have a lower tendency to recrystallize. Dendrimer substituents may be used to enhance the ability of small molecules to undergo solution processing.

Devices fabricated in accordance with embodiments of the invention may be incorporated into a wide variety of consumer products, including flat panel displays, computer monitors, televisions, billboards, lights for interior or exterior illumination and/or signaling, heads up displays, fully transparent displays, flexible displays, laser printers, telephones, cell phones, personal digital assistants (PDAs), laptop computers, digital cameras, camcorders, viewfinders, micro-displays, vehicles, a large area wall, theater or stadium screen, or a sign. Various control mechanisms may be used to control devices fabricated in accordance with the present invention, including passive matrix and active matrix. Many of the devices are intended for use in a temperature range comfortable to humans, such as 18 degrees C. to 30 degrees C., and more preferably at room temperature (20-25 degrees C.).

The materials and structures described herein may have applications in devices other than OLEDs. For example, other optoelectronic devices such as organic solar cells and organic photodetectors may employ the materials and structures. More generally, organic devices, such as organic transistors, may employ the materials and structures.

The terms halo, halogen, alkyl, cycloalkyl, alkenyl, alkynyl, arylkyl, heterocyclic group, aryl, aromatic group, and heteroaryl are known to the art, and are defined in U.S. Pat. No. 7,279,704 at cols. 31-32, which are incorporated herein by reference.

Dibenzo[b,d]thiophene (also referred to herein as “dibenzothiophene”)-containing materials are provided, which can be used in the PHOLED devices fabricated by both vapor deposition or solution processing, giving long lifetime stable devices with low voltage. The materials may be used as a stable host in PHOLED devices, or in other layers, such as an enhancement layer.

Compounds are provided comprising dibenzothiophene and/or dibenzofuran. Dibenzothiophenes and dibenzofurans may be used as hole and/or electron transporting organic conductors, they usually exhibit more reversible electrochemical reduction in solution than some common organic groups, such as biphenyl. The triplet energies of dibenzothiophenes and dibenzofurans are relatively high. Therefore, a compound containing dibenzothiophene and/or dibenzofuran may be advantageously used as a host or a material for an enhancement layer in PHOLED devices. For example, the triplet energy of dibenzothiophene is high enough for use in a blue or green PHOLED device. Dibenzothiophene and/or dibenzofuran-containing compounds may provide improved device stability while maintaining good device efficiency.

Dibenzothiophene-containing materials may have the following general structure:

Each of R₁ and R₂ may be independently selected from the group consisting of any alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, heteroaryl, and hydrogen, and where R₁ and R₂ may represent multiple substitutions.

Particular dibenzothiophene compounds are provided, which may be advantageously used in OLEDs, having the following structures:

Each of R₁ through R₆ are independently selected from the group consisting of any alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, heteroaryl, and hydrogen, and where each of R₁ through R₆ may represent multiple substitutions.

Additionally, particular dibenzothiophene-containing compounds, which may be advantageously used in OLEDs, are provided:

Dibenzothiophene-containing and/or dibenzofuran-containing compounds are provided, which may be advantageously used in OLEDs, having the following structures:

Each of R₁ through R₈ are independently selected from the group consisting of any alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, heteroaryl, and hydrogen, and where each of R₁ through R8 may represent multiple substitutions.

Additionally, dibenzothiophene-containing and/or dibenzofuran-containing compounds are provided, which may be advantageously used in OLEDs, are provided:

As used herein, the following compounds have the following structures:

Particular host-dopant combinations for the emissive layer of an OLED are also provided which may lead to devices having particularly good properties. Specifically, devices having an emissive layer using H1 as the host and P1, P2, or P7 as an emissive dopant are demonstrated to have particularly good properties. Such devices may be particularly favorable when the emissive layer includes two organic layers, a first organic layer including H1 doped with P1, and a second organic layer including H1 doped with P2, as illustrated in FIG. 3.

Similarly, devices having an emissive layer using Compound 1 as the host and P3, P4 and/or P5 as dopants may lead to devices having particularly good properties. Specifically, devices having an emissive layer using Compound 1 as the host and P3 as an emissive dopant, and/or an emissive layer with multiple dopants using Compound 1 as the host and P4 and P5 as dopants, where P5 is the primary emissive dopant in the layer. Such devices may be particularly favorable when the emissive layer includes two organic layers, a first organic layer including Compound 1 doped with P3, and a second organic layer including Compound 1 doped with P4 and P5, as illustrated in FIG. 9.

Devices having an emissive layer using Compound 23 as the host and P1 as the dopant may also lead to devices having particularly good properties.

Additionally, a consumer product comprising a device having an anode, a cathode, and an organic layer, disposed between the anode and the cathode. The organic layer further comprises a material containing a compound selected from the group consisting of Compound 2G-35G where R₁ through R₈ are independently selected from the group consisting of any alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, heteroaryl and hydrogen, and where each of R₁ through R₈ may represent multiple substitutions.

The materials described herein as useful for a particular layer in an organic light emitting device may be used in combination with a wide variety of other materials present in the device. For example, emissive dopants disclosed herein may be used in conjunction with a wide variety of hosts, transport layers, blocking layers, injection layers, electrodes and other layers that may be present. The materials described or referred to below are non-limiting examples of materials that may be useful in combination with the compounds disclosed herein, and one of skill in the art can readily consult the literature to identify other materials that may be useful in combination.

In addition to and/or in combination with the materials disclosed herein, many hole injection materials, hole transporting materials, host materials, dopant materials, exiton/hole blocking layer materials, electron transporting and electron injecting materials may be used in an OLED. Non-limiting examples of the materials that may be used in an OLED in combination with materials disclosed herein are listed in Table 1 below. Table 1 lists non-limiting classes of materials, non-limiting examples of compounds for each class, and references that disclose the materials.

TABLE 1 MATERIAL EXAMPLES OF MATERIAL PUBLICATIONS Hole injection materials Phthalocyanine and porphryin compounds

Appl. Phys. Lett. 69, 2160 (1996) Starburst triarylamines

J. Lumin. 72-74, 985 (1997) CF_(x) Fluorohydrocarbon polymer

Appl. Phys. Lett. 78, 673 (2001) Conducting polymers (e.g., PEDOT:PSS, polyaniline, polypthiophene)

Synth. Met. 87, 171 (1997) Arylamines complexed with metal oxides such as molybdenum and tungsten oxides

SID Symposium Digest, 37, 923 (2006) Hole transporting materials Triarylamines (e.g., TPD, α-NPD)

Appl. Phys. Lett. 51, 913 (1987)

US5061569

EP650955

J. Mater. Chem. 3, 319 (1993)

Appl. Phys. Lett. 90, 183503 (2007)

Appl. Phys. Lett. 90, 183503 (2007) Triaylamine on spirofluorene core

Synth. Met. 91, 209 (1997) Arylamine carbazole compounds

Adv. Mater. 6, 677 (1994) Indolocarbazoles

Synth. Met. 111, 421 (2000) Isoindole compounds

Chem. Mater. 15, 3148 (2003) Phosphorescent OLED host materials Red hosts Arylcarbazoles

Appl. Phys. Lett. 78, 1622 (2001) Metal 8-hydroxyquinolates (e.g., Alq₃, BAlq)

Nature 395, 151 (1998)

US20060202194

WO2005014551 Metal phenoxybenzothiazole compounds

Appl. Phys. Lett. 90, 123509 (2007) Conjugated oligomers and polymers (e.g., polyfluorene)

Org. Electron. 1, 15 (2000) Green hosts Arylcarbazoles

Appl. Phys. Lett. 78, 1622 (2001)

US2003175553

WO2001039234 Aryltriphenylene compounds

US20060280965

US20060280965 Polymers (e.g., PVK)

Appl. Phys. Lett. 77, 2280 (2000) Spirofluorene compounds

WO2004093207 Metal phenoxybenzooxazole compounds

WO05089025

WO06132173

JP200511610 Spirofluorene-carbazole compounds

JP2007254297

JP2007254297 Indolocabazoles

WO07063796

WO07063754 5-member ring electron deficient heterocycles (e.g., triazole, oxadiazole)

J. Appl. Phys. 90, 5048 (2001)

WO04107822 Metal phenoxypyridine compounds

WO05030900 Blue hosts Arylcarbazoles

Appl. Phys. Lett, 82, 2422 (2003)

US20070190359 Dibenzothiophene- carbazole compounds

WO2006114966 Phosphorescent dopants Red dopants Heavy metal porphyrins (e.g., PtOEP)

Nature 395, 151 (1998) Iridium(III) organometallic complexes

Appl. Phys. Lett. 78, 1622 (2001)

US06835469

US06835469

US20060202194

US20060202194

US07087321

US07087321

Adv. Mater. 19, 739 (2007) Platinum(II) organometallic complexes

WO2003040257 Osminum(III) complexes

Chem. Mater. 17, 3532 (2005) Ruthenium(II) complexes

Adv. Mater. 17, 1059 (2005) Green dopants Iridium(III) organometallic complexes

Inorg. Chem. 40, 1704 (2001)

US2002034656

US06687266

Chem. Mater. 16, 2480 (2004)

US2007190359

US 2006008670 JP2007123392

Adv. Mater. 16, 2003 (2004)

Angew. Chem. Int. Ed. 2006, 45, 7800 Pt(II) organometallic complexes

Appl. Phys. Lett. 86, 153505 (2005)

Appl. Phys. Lett. 86, 153505 (2005)

Chem. Lett. 34, 592 (2005) Gold complexes

Chem. Commun. 2906 (2005) Rhenium(III) complexes

Inorg. Chem. 42, 1248 (2003) Blue dopants Iridium(III) organometallic complexes

WO2002002714

WO2006009024

US2006251923

WO2006056418, US2005260441

US2007190359

US2002134984

Angew. Chem. Int. Ed. 47, 1 (2008)

Chem. Mater. 18, 5119 (2006)

Inorg. Chem. 46, 4308 (2007)

WO05123873

WO05123873

WO07004380

WO06082742 Osmium(II) complexes

US2005260449

Organometallics 23, 3745 (2004) Gold complexes

Appl. Phys. Lett. 74, 1361 (1999) Platinum(II) complexes

WO06098120, WO06103874 Exciton/hole blocking layer materials Bathocuprine compounds (e.g., BCP, BPhen)

Appl. Phys. Lett. 75, 4 (1999)

Appl. Phys. Lett. 79, 449 (2001) Metal 8-hydroxyquinolates (e.g., BAlq)

Appl. Phys. Lett. 81, 162 (2002) 5-member ring electron dificient heterocycles such as triazole, oxadiazole, imidazole, benzoimidazole

Appl. Phys. Lett. 81, 162 (2002) Triphenylene compounds

US20050025993 Fluorinated aromatic compounds

Appl. Phys. Lett. 79, 156 (2001) Electron transporting materials Anthracene- benzoimidazole compounds

WO03060956 Anthracene-benzothiazole compounds

Appl. Phys. Lett. 89, 063504 (2006) Metal 8-hydroxyquinolates (e.g., Alq₃)

Appl. Phys. Lett. 51, 913 (1987) Metal hydroxybenoquinolates

Chem. Lett. 5, 905 (1993) Bathocuprine compounds such as BCP, BPhen, etc

Appl. Phys. Lett. 91. 263503 (2007)

Appl. Phys. Lett. 79, 449 (2001) 5-member ring electron deficient heterocycles (e.g., triazole, oxadiazole, imidazole, benzoimidazole)

Appl. Phys. Lett. 74, 865 (1999)

Appl. Phys. Lett. 55, 1489 (1989)

Jpn. J. Apply. Phys. 32, L917 (1993) Silole compounds

Org. Electron. 4, 113 (2003) Arylborane compounds

J. Am. Chem. Soc. 120, 9714 (1998) Fluorinated aromatic compounds

J. Am. Chem. Soc. 122, 1832 (2000)

EXPERIMENTAL Compound Examples

Some of the dibenzothiophene-containing compounds were synthesized, as follows:

Step 1. 3,3′-dihydroxybiphenyl (9.3 g, 50 mmol) was dissolved in 100 mL of CH₂Cl₂, followed by the addition of pyridine (15.8 g, 200 mmol). To this solution at −15° C., Tf₂O (42.3 g, 150 mmol) was added dropwise. The mixture was continued to stir at room temperature for 5 h. The organic phase was separated and washed with brine once. The crude product was further purified by a silica column. 3,3′-ditriflatebiphenyl was obtained as pale white solid (21.3 g).

Step 2. To a 500 mL round flask was added 3,3′-ditriflatebiphenyl (2.7 g, 6 mmol), 4-dibenzothiopheneboronic acid (4.1 g, 18 mmol), Pd₂(dba)₃ (0.2 g, 0.2 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (0.3 g, 0.8 mmol), potassium phosphate tribasic (5.1 g, 24 mmol), and 150 mL of toluene. The reaction was heated to reflux and stirred under a nitrogen atmosphere for 24 hours. After cooling, the mixture was purified by a silica gel column. Yield was 2.6 g.

To a 500 mL round flask was added 2,2′-ditriflatebiphenyl (2.7 g, 6 mmol), 4-dibenzothiopheneboronic acid (4.1 g, 18 mmol), Pd₂(dba)₃ (0.2 g, 0.2 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (0.3 g, 0.8 mmol), potassium phosphate tribasic (5.1 g, 24 mmol), and 150 mL of toluene. The reaction was heated to reflux and stirred under a nitrogen atmosphere for 24 hours. After cooling, the mixture was purified by a silica gel column. Yield was 2.5 g.

To a 500 mL round flask was added 4,6-diiododibenzothiophene (4.2 g, 9.6 mmol), 4-dibenzothiopheneboronic acid (5.3 g, 23.1 mmol), Pd₂(dba)₃ (0.2 g, 0.2 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (0.3 g, 0.8 mmol), potassium phosphate tribasic (7.4 g, 35 mmol), and 150 mL of toluene. The reaction was heated to reflux and stirred under a nitrogen atmosphere for 24 hours. After cooling, the mixture was purified by a silica gel column. Yield was 2.4 g.

To a 500 mL round flask was added 4,6-diiododibenzothiophene (3.9 g, 8.9 mmol), carbazole (3.3 g, 19.6 mmol), Pd₂(dba)₃ (0.2 g, 0.2 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (0.3 g, 0.8 mmol), sodium t-butoxide (5.8 g, 60 mmol), and 200 mL of xylene. The reaction was heated to reflux and stirred under a nitrogen atmosphere for 24 hours. After cooling, the mixture was purified by a silica gel column. Yield was 2.2 g.

Step 1. 2,6-Dibromo-1,3,5-trimethylbenzene (8.34 g, 30 mmol) was dissolved in 50 ml of CHCl₃ and suspended with 1.0 g of iron powder in 200 ml round-bottom flask. Bromine (2.00 ml, 31 mmol) was added dropwise at room temperature and reaction mixture was heated to reflux for 3 hours, cooled down to room temperature and stirred overnight. Solution was decanted, washed with NaOH 10% aq., filtered and evaporated. The solid residue was crystallized from chloroform, providing 7.00 g of yellow solid (2,4,6-tribromo-1,3,5-trimethylbenzene).

Step 2. The 1 L round-bottom flask equipped with magnetic stirrer and reflux condenser was charged with 2,4,6-tribromo-1,3,5-trimethylbenzene (3.4 g, 9.5 mmol), 4-dibenzothiopheneboronic acid (8.7 g, 38 mmol), Pd₂(OAc)₂ (0.16 g, 0.7 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (0.46 g, 1.1 mmol), potassium phosphate tribasic (53 g, 250 mmol), 1.2 ml of water and 700 mL of toluene. The reaction was heated to reflux and stirred under a nitrogen atmosphere for 24 hours. After cooling, the mixture was purified by a silica gel column. Yield was 5.2 g.

To a 500 mL round flask was added cyanuric chloride (1.5 g, 8.0 mmol), 4-dibenzothiopheneboronic acid (6.8 g, 30 mmol), Pd₂(dba)₃ (0.2 g, 0.2 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (0.3 g, 0.8 mmol), potassium phosphate tribasic (8.5 g, 40 mmol), and 250 mL of toluene. The reaction was heated to reflux and stirred under a nitrogen atmosphere for 24 hours. After cooling, the mixture was filtered. The product was further purified by recrystallization from EtOAc. Yield was 3.0 g.

2,8-Dibromobenzothiophene (2.5 g, 7.3 mmol) in 150 mL of THF was treated with n-BuLi (1.6 M in hexane, 10 mL, 16 mmol) at −78° C. for 1 h. Dimesitylboron fluoride (5.0 g, 16.8 mmol) in 40 mL of ether was added dropwise. After the mixture was stirred for another 1 h, the mixture was slowly warmed up to room temperature and continued to stir overnight. The product was purified by a silica gel column. Yield was 2.8 g.

4-Dibenzothiopheneboronic acid (5.0 g) was suspended in 300 mL of xylene and performed the Dean-Stark extraction for 5 h. After cooling down, the solid was collected, washed with EtOAc and hexane, and sublimed at 320° C. twice. Yield was 3.6 g.

To a 500 mL round flask lithium amide (0.2 g, 10 mmol), 4-iododibenzothiophene (9.9 g, 32 mmol), Pd₂(dba)₃ (0.2 g, 0.2 mmol), 2-dicyclohexylphosphino -2′,4′,6′-triisopropylbiphenyl (0.4 g, 0.8 mmol), sodium t-butoxide (2.9 g, 30 mmol), and 200 mL of toluene were added. The reaction was heated to reflux and stirred under a nitrogen atmosphere for 24 hours. After cooling, the mixture was purified by a silica gel column. Yield was 4.0 g.

The 500 mL round flask was charged with 2,3-dibromobenzo[b]thiophene (5.0 g, 17.1 mmol), 4-dibenzothiopheneboronic acid (10.0 g, 43.8 mmol), Pd₂(PPh₃)₄ (0.8 g, 0.7 mmol), potassium carbonate (14.2 g, 103 mmol) in 30 ml water followed by 200 ml of toluene. The reaction was heated to reflux and stirred under a nitrogen atmosphere for 24 hours. After cooling, separation of aqueous phase and evaporation the mixture was purified by a silica gel column (hexane/ethyl acetate 4/1 mixture), providing target compound as solidified colorless oil (4.6 g).

Step 1. Dibenzothiophene (9.21 g, 50 mmol) was dissolved in 100 ml of dry THF and solution was cooled to −50° C. n-BuLi (1.6 molar solution in hexanes, 40 ml, 64 mmol) was added dropwise. The reaction mixture was warmed to room temperature, stirred for 4 hours and cooled to −30° C. Dibenzofluorenone (9.0 g, 50 mmol) in 70 ml THF was added dropwise, reaction mixture was allowed to warm to room temperature and stirred overnight. The reaction mixture was diluted with ethyl acetate (75 ml), washed with brine 3 times, dried over MgSO₄, filtered and evaporated. The solid residue was purified by column chromatography on silica (hexane/ethyl acetate 7/3) providing 12.0 g of 9-(dibenzo[b,d]thiophen-4-yl)-9H-fluoren-9-ol as white solid.

Step 2. 9-(Dibenzo[b,d]thiophen-4-yl)-9H-fluoren-9-ol (product from the Step 1, 3.64 g, 10 mmol) were dissolved in 100 ml of dry toluene. Twenty drops of 10% solution of P₂O₅ in CH₃SO₃H were added at room temperature, and reaction mixture was stirred for 5 hours. The solution was decanted from solid residue, filtered through silica plug and evaporated. The solid residue was subjected to column chromatography (silica, hexane/ethyl acetate 4/1) providing 4.0 g of white solid.

Step 1. The 200 ml round-bottom flask equipped with reflux condenser and magnetic stirrer was charged with carbazole (14.75 g, 88 mmol), 3-iodobromobenzene (25.0 g, 88 mmol), Pd₂(dba)₃ (0.8 g, 0.85 mmol) and dppf (1,1′-bis(diphenylphosphino)ferrocene, 0.98 g, 1.8 mmol), sodium t-buthoxide (25 g, 265 mmol) and 100 ml of dry xylene. Reaction mixture was refluxed under N₂ atmosphere for 48 hours, cooled down to room temperature and evaporated. The solid residue was subjected to column chromatography on silica (eluent —hexane/ethyl acetate 9/1) providing 11.7 g of 9-(3-bromophenyl) -9H-carbazole as white solid.

Step 2. 9-(3-Bromophenyl)-9H-carbazole (11.7 g, 36 mmol), Bis(pinacolato)diboron (13.85 g, 54 mmol), potassium acetate (7.00 g, 71 mmol), 1,1′-bis(diphenylphosphino)ferrocene]dichloropalladium (II) (0.6 g) were dissolved in 100 ml of dry dioxane and refluxed under N₂ atmosphere overnight. Then reaction mixture was cooled down to room temperature, diluted with ethyl acetate, washed with brine, dried over magnesium sulfate, and evaporated. The solid residue was subjected to column chromatography on silica (eluent hexane/ethyl acetate 5/1), providing 8.00 of 9-(3-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)phenyl)-9H-carbazole as yellow solid. Analytically pure material may be prepared by crystallization from hexane, otherwise product was used without additional purification.

Step 3. 2-Bromoanisole (5.61 g, 30 mmol) and 4-dibenzothiopheneboronic acid (6.84 g, 30 mmol), Pd₂(PPh₃)₄(1.00 g, 0.8 mmol) were dissolved in 100 ml of toluene. Saturated solution of sodium carbonate (12.5 g in water) was added, and reaction mixture was heated to reflux under N₂ atmosphere overnight. Then reaction mixture was cooled down to room temperature, separated organic phase and evaporated toluene. The solid residue was subjected to column chromatography on silica (eluent—hexane/ethyl acetate 4/1) providing 4-(2-methoxyphenyl)dibenzo[b,d]thiophene as 6.6 g of colorless solidified oil.

Step 4. 4-(2-Methoxyphenyl)dibenzo[b,d]thiophene (6.6 g, 23 mmol) and pyridinium hydrochloride (27 g, 230 mmol) were mixed together, placed in the 100 ml round bottom flask and heated to reflux for 45 min. Reaction mixture was cooled to 60° C., diluted with 100 ml water and extracted with ethyl acetate. The organic phase was separated, dried over magnesium sulfate, filtered and evaporated. The residue was subjected to column chromatography on silica (eluent hexane/ethyl acetate 5/1), providing 4.00 g of 2-(dibenzo[b,d]thiophen-4-yl)phenol as clear solidified oil.

Step 5. 2-(Dibenzo[b,d]thiophen-4-yl)phenol (3.9 g, 14 mmol) was dissolved in 80 ml of dry dichloromethane, containing 5 ml of dry pyridine, and solution was cooled in the ice bath. The triflic anhydride (5 ml, 28 mmol) was added dropwise, the reaction mixture was stirred overnight at room temperature, washed with water and evaporated. The residue was purified by column chromatography on silica (eluent hexane/ethyl acetate 9/1), providing 4.2 g of clear colorless solidified oil.

Step 6. The 200 ml round bottom flask with reflux condenser and magnetic stirrer was charged with triflate from Step 5 (4.1 g, 10 mmol) and boronic ester from Step 2 (3.7 g, 10 mmol) followed by tribasic potassium phosphate (6.36 g, 30 mmol), palladium acetate (0.67 g, 0.3 mmol), ), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (0.8 g, 0.6 mmol), 200 ml of toluene and 6 ml of water. The reaction was heated to reflux and stirred under a nitrogen atmosphere for 24 hours. After cooling, the mixture was purified by a silica gel column with eluent hexane/ethyl acetate 4/1, providing 2.8 g of target compound as white solid.

To a 500 mL round flask carbazole (3.7 g, 22 mmol), 2,8-dibromobenzothiophene (3.4 g, 10 mmol), Pd(OAc)₂ (0.1 g, 0.5 mmol), tri-t-butylphosphine (1 M in toluene, 1.5 mL, 1.5 mmol), sodium t-butoxide (6.3 g, 66 mmol), and 200 mL of xylene were added. The reaction was heated to reflux and stirred under a nitrogen atmosphere for 24 hours. After cooling, the mixture was purified by a silica gel column. Yield was 4.7 g.

To a 500 mL round flask 4-iododibenzothiophene (6.2 g, 20 mmol), carbazole (4.0 g, 24 mmol), Pd₂(dba)₃ (0.9 g, 1.0 mmol), 2-dicyclohexylphosphino-2′,6′-dimethoxybiphenyl (1.6 g, 4.0 mmol), sodium t-butoxide (5.8 g, 60 mmol), and 200 mL of xylene were added. The reaction was heated to reflux and stirred under a nitrogen atmosphere for 24 hours. After cooling, the mixture was purified by a silica gel column. Yield was 2.4 g.

m-Carborane (5.0 g, 35 mmol) in 200 mL of dry DME was treated with n-BuLi (1.6 M in hexane, 48 mL, 76 mmol) at 0° C. for 30 min under nitrogen. After the mixture was warm up to room temperature, CuCl (9.5 g, 96 mmol) was added. The mixture continued to stir for 1 h, and 30 mL of dry pyridine, 4-iododibenzothiophene (22.6 g, 73 mmol) were added. The resulting mixture was refluxed for 60 h. After cooling, the mixture was purified by a silica gel column. Yield was 1.8 g.

Step 1. Dibenzothiophene (27 g, 147 mmol) in 400 mL of THF was treated slowly with n-BuLi (1.6 M in hexane, 100 mL, 160 mmol) at −50° C. The resulting mixture was slowly warmed up to room temperature and continued to stir for 5 h. The solution was cooled back to −78° C., DMF (61 mL) in 100 mL of THF was added slowly. The mixture continued to stir for another 2 h at this temperature and then warmed up to room temperature. The product was extracted with EtOAc and further purified by a silica gel column. Yield of 4-dibenzothiophenealdhyde was 21 g.

Step 2. To a 300 mL of THF solution of 2,8-dibromodibenzothiophene (3.4 g, 10 mmol) at −78° C. was added slowly by n-BuLi (1.6 M in hexane, 13.8 mL, 22 mmol). After stirred for 1 h at this temperature, the mixture was treated slowly with a 100 mL of THF solution of 4-dibenzothiophenealdhyde (4.2 g, 20 mmol). The solution was then allowed to warm up to room temperature. The product was extracted with EtOAc and further purified by a silica gel column. Yield of dicarbinol intermediate was 4.2 g.

Step 3. To a 50 mL of CH₂Cl₂ solution of above dicarbinol intermediate (4.5 g, 7.4 mmol) and CF₃COOH (60 mL) was added portionwise of solid powder of sodium borohydride (2.8 g, 74 mmol. The mixture was stirred under nitrogen overnight. The solvents was removed by rotovap, and the solid was washed with water then with NaHCO₃ solution. The crude product was further purified by a silica gel column. Yield of final product was 2.4 g.

Dibenzothiophene (14 g, 76 mmol) in 200 mL of THF was treated slowly with n-BuLi (1.6 M in hexane, 50 mL, 80 mmol) at −50° C. The resulting mixture was slowly warmed up to room temperature and continued to stir for 5 h. The solution was cooled back to −78° C., SiCl₄ (2.0 g, 12 mmol) was added slowly. The mixture continued to stir for another 2 h at this temperature and 12 h at room temperature. The product was extracted with EtOAc and further purified by a silica gel column. Yield was 3.5 g.

To a 500 mL round flask 3,6-di(9-carbazolyl)carbazole (3.0 g, 6 mmol, prepared similarly as described above for 3-(9-carbazolyl)carbazole), 2-bromobenzothiophene. (2.1 g, 7.8 mmol), CuI (0.4 g, 2.0 mmol), trans-1,2-Diaminocyclohexane (0.4 g, 3.6 mmol), potassium phosphate tribasic (3.2 g, 15 mmol), and 250 mL of toluene were added. The reaction was heated to reflux and stirred under a nitrogen atmosphere for 24 hours. After cooling, the mixture was purified by a silica gel column. Yield was 3.1 g.

The 300 mL round bottom flask, equipped with magnetic stirrer and refluxed condenser, was charged with carbazole (7.1 g, 42.5 mmol), 3-iodobromobenzene (25.00 g, 88 mmol), Pd₂(dba)₃ (800 mg, 1 mol %), dppf (1′,1′-bis(diphenylphosphino)ferrocene (975 mg, 2 mol %), sodium t-buthoxide (6.3 g) and m-xylene (100 ml). The reaction mixture was heated to reflux and stirred under nitrogen atmosphere for 48 hours. Then reaction was cooled down to room temperature, filtered through silica plug and evaporated. The residue was subjected to column chromatography on silica gel, eluent gradient mixture hexane —hexane/ethyl acetate mixture 9:1, providing 7.00 g of 9-(3-bromo -phenyl) -9H-carbazole as white solid, structure was confirmed by NMR and GCMS spectroscopy.

7.00 g of 9-(3-bromo-phenyl)-9H-carbazole (21.7 mmol), bis-pinacolatodiborane (8.3 g, 32.7 mmol), potassium acetate (4.30 g) and (1,1′-bis(diphenylphosphino) -ferrocene)dichloropalladium (II) (500 mg) were dissolved in 100 ml of dioxane and refluxed under nitrogen for 24 hours. After evaporation the residue was subjected to column chromatography on silica gel (eluent hexane/ethyl acetate 9/1 mixture), providing pure 9-[3-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-phenyl]-9H-carbazole as white solid (11.8 g).

The 300 mL round bottom flask, equipped with magnetic stirrer and refluxed condenser, was charged with 2,8-dibromo-dibenzothiophene (3.42 g, 10 mmol), 9-[3-(4,4,5,5-tetramethyl-[1,3,2]dioxaborolan-2-yl)-phenyl]-9H-carbazole (11.7 g, 30 mmol), palladium (II) acetate (64 mg,), 2-dicylohexylphosphino-2′,6′-dimethoxybiphenyl (234 mg), potassium phosphate tribasic anhydrous (53.0 g), 700 ml of toluene and 2 ml of water. The reaction mixture was heated to reflux and stirred under nitrogen atmosphere for 24 hours. Then reaction was cooled down to room temperature, filtered through silica plug and evaporated. The residue was washed with hexane, ethanol, water, ethanol and hexane, then was crystallized from toluene. Sublimation (255° C. at 10⁻⁵ mm Hg) provided pure material (white solid, 2.0 g, structure confirmed by NMR.

2,6-Dimethoxyaniline (5.5 g, 0.036 mol), 2,2′-dibromobiphenyl (13.45 g, 0.043 mol), sodium tert-butoxide (8.58 g, 0.089 mol) and Pd₂(dba)₃ (1.15 g, 13 mmol) were charged into a 500 mL 3-neck flask with 300 mL of anhydrous toluene. This flask was evacuated and back filled with N₂ (this procedure was repeated a total of 3 times). Lastly, (9.6 mL, 96 mmol) P(t-Bu)₃ 1.0 M in toluene was syringed into the reaction vessel through a septum. The reaction mixture was heated at reflux for 18 h. Heating was then discontinued. The reaction mixture was diluted with 200 mL of water. The toluene layer was separated. The aqueous was extracted 1×200 mL toluene. The toluene extracts were combined, were dried over magnesium sulfate then were filtered and concentrated under vacuum. Silica gel chromatography of the crude product. Solvent system used was 20-35% methylene chloride/hexanes.

9-(2,6-Dimethoxyphenyl)-9H-carbazole (10.00 g) and pyridinium hydrochloride (50.0 g) were placed in the 250 ml round-bottom flask, equipped with magnetic stirrer and immersed in the pre-heated oil bath (230° C., 45 min). The reaction mixture was cooled down to room temperature, diluted with 400 ml water and extracted with ethyl acetate (3×150 ml). Organic fractions were combined, dried over sodium sulfate anhydrous, filtered and evaporated, providing 5.5 g of pure 2-carbazol-9-yl-benzene-1,3-diol. 2-Carbazol-9-yl -benzene-1,3-diol (5.5. g, 20 mmol) and pyridine (6.0 ml) were dissolved in 50 ml DCM (anhydrous) and cooled in the ice bath. Solution of triflic anhydride (6.0 ml) in 20 ml DCM was added dropwise upon intensive stirring, reaction mixture was warmed up to room temperature and stirred overnight. The reaction mixture was washed with water, dried over sodium sulfate, filtered and evaporated, providing crude triflate. Pure material (white solid, 6.0 g) was obtained by column chromatography on silica gel (eluent hexane/ethyl acetate 1/1 mixture).

Bis-triflate (3.13 g, 5.8 mmol), 4-dibenzothiopheneboronic acid (3.30 g, 14.5 mmol), Pd₂(dba)₃ (212 mg, 2 mol %), 2-dicylohexylphosphino 2′,6′-dimethoxybiphenyl (190 mg, 4 mol %), potassium phosphate tribasic monohydrate (8.00 g), 100 ml of toluene and 1 ml of water were refluxed in the round-bottom flask under nitrogen atmosphere for 24 hours, filtered hot through silica plug and evaporated. The residue was washed with hexane, ethanol, water, ethanol and hexane, then crystallized from toluene, providing pure material (4.1 g).

2,6-Dimethoxyphenol (15.4 g, 0.1 mol) and 15 ml of pyridine were dissolved in 150 ml DCM and solution was cooled in the ice bath. Triflic anhydride was added dropwise upon vigorous stirring, reaction mixture was allowed to warm up to room temperature, washed with water and evaporated. Kugelrohr distillation (200° C., 2 mm Hg) provided 25 g of solidified clear oil.

2,6-Dimethoxytriflate (8.58 g, 30 mmol), 4-dibenzothiopheneboronic acid (6.84 g, 30 mmol), potassium phosphate tribasic monohydrate (20.7 g), palladium (II) acetate (672 mg), 2-dicylohexylphosphino-2′,6′-dimethoxybiphenyl (700 mg) and 150 ml of toluene and 3 ml of water were heated to reflux and stirred under nitrogen atmosphere for 24 hours. Hot reaction mixture was filtered through silica plug and evaporated, the residue was subjected to column chromatography on silica (eluent hexane/ethyl acetate 4/1 mixture), providing 4-(2,6-dimethoxyphenyl)-dibenzothiophene (9.00 g, prism crystals from ethyl acetate).

4-(2,6-Dimethoxyphenyl)-dibenzothiophene (9.00 g) and pyridinium hydrochloride (20 g) were placed in the 100 mL round-bottom flask, equipped with a magnetic stirrer. The flask was immersed in the pre-heated oil bath (220° C., 1 hour), cooled down to room temperature and dissolved in 200 ml of water. The solution was extracted with ethyl acetate (4×50 mL), organic fractions were combined, dried over sodium sulfate, filtered and evaporated, providing 2-(dibenzo[b,d]thiophen-4-yl)benzene-1,3-diol (7.2 g, white solid).

2-(Dibenzo[b,d]thiophen-4-yl)benzene-1,3-diol (7.2 g) was dissolved in 150 mL of dry DCM, containing 15 mL of pyridine. Solution was cooled in the ice bath, then triflic anhydride (18 mL in 25 mL of DCM) was added dropwise. Reaction was allowed to warm up to room temperature and washed with 10% sodium bicarbonate solution in water. DCM was evaporated, and the residue was subjected to column chromatography, providing 14.5 g of bis-triflate.

Triflate (5.56 g, 10 mmol), 4-dibenzothiopheneboronic acid (5.35 g, 25 mmol), palladium (II) acetate (44 mg), 2-dicylohexylphosphino-2′,6′-dimethoxybiphenyl (161 mg) and potassium phosphate tribasic trihydrate (7.00 g) were suspended in 100 ml of toluene and refluxed under nitrogen atmosphere for 24 hours. Hot reaction mixture was filtered and evaporated, the residue was crystallized from toluene twice. Sublimation (245° C., 10⁻⁵ mm Hg) provided 5.0 g of target compound.

The 300 ml round-bottom flask equipped with reflux condenser and magnetic stirrer was charged with 2,6-dimethoxytriflate (10.00 g, 35 mmol), phenyl boronic acid (4.25 g, 35 mmol), potassium phosphate tribasic monohydrate (24.1 g), palladium (II) acetate (156 mg, 2 mol %), 2-dicylohexylphosphino-2′,6′-dimethoxybiphenyl (573 mg, 4 mol %), toluene (100 ml) and water (2 ml). The reaction mixture was refluxed overnight, filtered through silica plug and evaporated. The residue was subjected to column chromatography on silica gel (eluent hexane/ethyl acetate 4/1 mixture), providing dimethoxybiphenyl as white solid (5.00 g).

2,6-Dimethoxybiphenyl (5.00 g) and 15 g of pyridinium hydrochloride were placed in the round-bottom flask and immersed in the oil bath (210° C., 1.5 hours). Then the reaction was cooled down to room temperature, diluted with 200 ml of water and extracted with ethyl acetate (4×50 ml). Organic fractions were combined, dried over sodium sulfate and evaporated. The residue was subjected to column chromatography on silica gel (eluent hexane/ethyl acetate 1/1 mixture), providing 3.3 of biphenyl-2,6-diol as yellow solid.

Biphenyl-2,6-diol (7.2 g, 39 mmol) was dissolved in DCM (100 ml) and pyridine (10 ml). The solution was cooled in the ice bath, and triflic anhydride (27.3 g) was added dropwise upon vigorous stirring. The reaction mixture was allowed to warm up to room temperature, was washed with water, dried and evaporated. The residue was subjected to column chromatography on silica gel (eluent hexane/ethyl acetate 4/1 mixture), providing 8.00 g of pure triflate.

The triflate (7.4 g, 16.4 mmol), 4-dibenzothiophene boronic acid (11.2 g, 49 mmol), potassium phosphate tribasic monohydrate (22.7 g), palladium (II) acetate (70 mg), 2-dicylohexylphosphino-2′,6′-dimethoxybiphenyl (270 mg) and 100 ml of toluene were refluxed overnight under nitrogen atmosphere. The hot solution was filtered through silica plug and evaporated. The residue was crystallized hexane/ethyl acetate, providing target product as white solid (5.01 g). The material was additionally purified by sublimation (220° C., 10⁻⁵ mm Hg).

The 300 ml round-bottom flask equipped with reflux condenser and magnetic stirrer was charged with 2-bromoaniline (8.00 g, 46.5 mmol), 4-dibenzothiopheneboronic acid (10.5 g, 46.5 mmol), potassium carbonate (20 g, saturated solution in water), tetrakis(triphe-nylphoshine)palladium (0) (500 mg) and 100 ml of toluene. The reaction mixture was refluxed overnight under nitrogen atmosphere, filtered through silica plug and evaporated. Product was purified by column chromatography on silica gel, eluent hexane/ethyl acetate 4/1 mixture, providing 2-(dibenzo[b,d]thiophen-4-yl)aniline (10.1 g) as yellow oil.

2-(Dibenzo[b,d]thiophen-4-yl)aniline (10.1 g, 36.4 mmol), 2,2′-dibromobiphenyl (12.0 g, 38.5 mmol), sodium tert-butoxide (7.00 g, 72.9 mmol), and Pd₂(dba)₃ (330 mg) were charged into a 500 mL 3-neck flask with 300 mL of anhydrous toluene. This flask was evacuated and back filled with N₂ (this procedure was repeated a total of 3 times). Lastly, (5 mL, 96 mmol) P(t-Bu)₃ 1.0 M in toluene was syringed into the reaction vessel through a septum. The reaction mixture was heated at reflux for 18 h. Heating was then discontinued. The reaction mixture was diluted with 200 mL of water. The toluene layer was separated. The aqueous was extracted 1×200 mL toluene. The toluene extracts were combined, were dried over magnesium sulfate then were filtered and concentrated under vacuum. Crude material was washed with hexane and crystallized from toluene-DCM. The material was additionally purified by sublimation (190° C., 10⁻⁵ mm Hg), providing 6.23 g of pure crystalline material.

The 300 mL round-bottom flask equipped with magnetic stirrer and reflux condenser was charged with 2,6-dibromopyridine (2.20 g, 9.2 mmol), 4-dibenzothiopheneboronic acid (4.62 g, 20 mmol), Pd₂(dba)₃ (180 mg), S-phos (220 mg), potassium triphosphate (6.00 g) and 100 mL of anhydrous toluene. The flask was filled with nitrogen, and solution was stirred under reflux overnight. Then hot reaction mixture was filtered through silica plug, silica was washed with hot toluene. Organic fractions were combined and evaporated. The residue was subjected to column chromatography on silica gel (eluent hexane/ethyl acetate 4/1 mixture), providing target compound as white solid (3.01 g). Material was additionally purified by sublimation (225° C. at 10⁻⁵ mm Hg) and used for device fabrication.

Device Examples

All example devices were fabricated by high vacuum (<10⁻⁷ Torr) thermal evaporation. The anode electrode is ˜800 Å, 1200 Å or 2000 Å of indium tin oxide (ITO), or 800 Å Sapphire/IZO. The cathode consists of 10 Å of LiF followed by 1000 Å of Al. All devices are encapsulated with a glass lid sealed with an epoxy resin in a nitrogen glove box (<1 ppm of H₂O and O₂) immediately after fabrication, and a moisture getter was incorporated inside the package.

The organic stack of Device Examples 1-8 consisted of sequentially, from the ITO surface (1200 Å), 100 Å of P1 as the hole injection layer (HIL), 300 Å of 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (α-NPD) as the hole transporting layer (HTL), 300 Å of the invention compound doped with 10 or 15 wt % of an Ir phosphorescent compound as the emissive layer (EML), 50 Å or 100 Å of HPT or the invention compound as the ETL2 and 400 or 450 Å of tris-8-hydroxyquinoline aluminum (Alq₃) as the ETL1.

Comparative Example 1 was fabricated similarly to the Device Examples except that CBP was used as the host.

The materials for the Emissive Layer, and the materials and thicknesses for ETL 2 and ETL1, of Device Examples 1-8 are provided in Table 2. The devices were tested, and the results measured are provided in Table 3. Compound is abbreviated using the term Cmpd.

TABLE 2 ITO Device Dopant thickness Example Host wt % ETL2 (Å) ETL1 (Å) (Å) Comparative 1 CBP P1 10% HPT (50) Alq₃ (450) 1200 1 Cmpd 1 P1 10% Cmpd 1 Alq₃ (400) 1200 (100) 2 Cmpd 1 P6 10% Cmpd 1 Alq₃ (400) 1200 (100) 3 Cmpd 1 P1 10% HPT (50) Alq₃ (450) 1200 4 Cmpd 1 P6 10% HPT (50) Alq₃ (450) 1200 5 Cmpd 2 P1 9% HPT (50) Alq₃ (400) 800 6 Cmpd 3 P1 9% HPT (50) Alq₃ (400) 800 7 Cmpd 4 P1 9% HPT (50) Alq₃ (400) 1200 8 Cmpd 5 P1 9% HPT (50) Alq₃ (400) 1200

TABLE 3 At J = At L = 1000 cd/m² 40 mA/cm² Device CIE Emission FWHM LE EQE PE L₀ LT_(80%) Example X Y max (nm) (nm) V (V) (cd/A) (%) (lm/W) (cd/m²) (hr) Comparative 1 0.346 0.613 522 75 6.2 57.0 16 28.9 13,304 105 1 0.337 0.619 523 73 7.4 48.2 13 20.5 13,611 325 2 0.328 0.620 520 73 7.4 36.8 10 15.6 12,284 340 3 0.338 0.618 524 73 6.3 60.3 17 30.1 13,683 300 4 0.328 0.621 520 73 6.4 52 14.4 25.5 14,014 187 5 0.336 0.623 524 72 5.9 53.8 15 28.7 16389 18 6 0.349 0.614 528 73 6.1 45.5 12 23.2 15672 28 7 0.355 0.609 528 74 6.8 39.6 11 18.3 13403 98 8 0.353 0.613 528 72 6.3 49.5 14 24.7 15442 5.5

From Device Examples 1-8, it can be seen that the Invention Compounds as hosts in green phosphorescent OLEDs give high device efficiency (LE>35 cd/A at 1000 cd/m²), indicating dibenzothiophene as a chromophore has triplet energy high enough for efficient green electrophosphorescence. Most notably is the high stability of the device incorporating Compounds 1 as the host. Device Example 3 and Comparative Example 1 are only different in the host. Device Example 3 uses Compound 1 as the host whereas Comparative Example 1 uses the commonly used host CBP. The lifetime, T_(80%) (defined as the time required for the initial luminance, L₀, to decay to 80% of its value, at a constant current density of 40 mA/cm² at room temperature) are 300 hours and 105 hours respectively, with Device Example 3 having a slightly higher L₀. This translates to almost a 3 fold improvement in the device stability. The invention compounds may function well as the enhancement layer (ETL2). Device Example 1 and Device Example 3 both have Compound 1 as the host, but Compound 1 and 2,3,6,7,10,11-hexaphenyltriphenylene (HPT) as the enhancement layer respectively. They have T_(0.8) of 325 and 300 hours respectively with similar L₀ (˜13600 cd/m²), indicating the good performance of the invention compound as the enhancement layer.

The data suggest that arylbenzothiophenes, particularly biphenyl substituted dibenzothiophenes, are excellent hosts and enhancement layer for phosphorescent OLEDs, providing as least the same efficiency and multiple times of improvement in stability compared to the commonly used CBP as the host.

A number of devices were fabricated having two different doped emissive layers, where the devices do not include a hole transport layer using a material such as NPD. Table 4 shows the structures for these devices. Table 5 shows measured experimental results for these devices. In general, the devices had an ITO anode, a hole injection layer of LG101™ (purchased from LG Chemical, Korea), and an emissive layer having a first organic layer and a second organic layer with an interface in between. Some of the devices had an enhancement layer (ETL2). All of the devices had an electron transport layer (ETL1) of LG201, available from the same source as LG101. Devices 9-16 have first and second organic layers with the same non-emissive materials, and different phosphorescent materials, where the first organic layer additionally includes a lower energy emissive material. All of devices 9-16 include emissive layers having a first and second organic layer with an interface in between. In all of these devices, the concentration of phosphorescent material is higher in the first (closer to anode) organic layer. The materials and thicknesses for Device Examples 9-16 are provided in Table 4. The devices were tested, and the results measured are provided in Table 5. Compound is abbreviated using the term Cmpd. All percentages are wt % unless otherwise noted.

TABLE 4 Device Anode HIL EML1 EML2 ETL2 ETL1 9 ITO LG101 Cmpd 1: Cmpd 1: P3 (18%) none LG201 [1200 Å] [100 Å] P4 (30%):P5 (0.5%) [300 Å] [250 Å] [300 Å] 10 ITO LG101 Cmpd 1: Cmpd 1: P3 (12%) none LG201 [1200 Å] [100 Å] P4 (30%):P5 (0.5%) [300 Å] [250 Å] [300 Å] 11 ITO LG101 Cmpd 1: Cmpd 1: P3 (24%) none LG201 [1200 Å] [100 Å] P4 (30%):P5 (0.5%) [300 Å] [250 Å] [300 Å] 12 ITO LG101 Cmpd 1: Cmpd 1: P3 (24%) Cmpd 1 [50 Å] LG201 [1200 Å] [100 Å] P4 (30%):P5 (0.5%) [300 Å] [250 Å] [300 Å] 13 ITO LG101 Cmpd 1: Cmpd 1: P3 (18%) Cmpd 1 [50 Å] LG201 [1200 Å] [100 Å] P4 (30%):P5 (0.5%) [300 Å] [250 Å] [300 Å] 14 ITO LG101 Cmpd 1: Cmpd 1: P3 (12%) Cmpd 1 [50 Å] LG201 [1200 Å] [100 Å] P4 (30%):P5 (0.5%) [300 Å] [250 Å] [300 Å] 15 ITO LG101 Cmpd 1: Cmpd 1: P3 (18%) Cmpd 1 [50 Å] LG201 [1200 Å] [200 Å] P4 (30%):P5 (0.5%) [200 Å] [250 Å] [300 Å] 16 ITO LG101 Cmpd 1: Cmpd 1: P3 (18%) Cmpd 1 [50 Å] LG201 [1200 Å] [100 Å] P4 (30%):P5 (0.5%) [200 Å] [250 Å] [300 Å]

TABLE 5 At 1,000 cd/m² At 10 V LE EQE PE mA/cm² At L₀ = 1,000 cd/m² Device (V) (cd/A) (%) (lm/W) CIE x CIE y LT_(70%) (hr) LT_(60%) (hr) 9 6.1 23.7 10.9 12.3 0.467 0.457 Not measured Not measured 10 6.2 31.7 15.1 16.1 0.500 0.445 35,500 100,000 11 6.2 14.9 6.9 7.5 0.467 0.457 Not measured Not measured 12 6.1 29.5 13.5 15.2 0.456 0.460 78,000 140,000 13 6.3 32.4 15.3 16.1 0.437 0.451 90,000 230,000 14 7.0 33.2 16.3 15.0 0.505 0.439 88,000 180,000 15 6.4 29.0 13.9 14.3 0.472 0.449 Not measured Not measured 16 6.2 29.4 14.2 14.9 0.467 0.448 Not measured Not measured

From Device Examples 9, 10 and 11, it can be seen that the efficiency of the device decreased with increasing concentration of P3, and the device CIE red-shifted with decreasing P3 concentration. Device Examples 9-11 differ only in the concentration of the emissive compound P3 (i.e., devices contain varying concentrations of P3) as all of Device Examples 9-11 contained Inventive Compound 1 as the host, and were without a blocking layer between the EML and the LG201.

From Device Examples 12, 13, and 14, it can be seen that the efficiency of the device decreased with increasing concentration of P3, the device CIE red-shifted with decreasing P3 concentration, and device operating voltage increased with decreasing concentration of P3. Devices 12-14 differ only in the concentration of the emissive compounds P3, as all of devices 12-14 contained the inventive Compound 1 as the host and the blocking layer situated between the EML and ETL. Notably, Compound 1 is an efficient electron transport and blocking layer material, because the efficiency of each of Devices 12, 13, and 14 was shown to exceed that of Devices 9, 10, and 11. Also, the electron stability of Compound 1 was found to be significant, because Devices 12-14 demonstrated an LT_(60%) stability that exceeded 100,000 hrs from 1,000 cd/m² initial luminance.

From Device Examples 15 and 16, it can be seen that the devices show variation in device characteristics (e.g., CIE, efficiency) when the injection layer LG101 thickness is varied (e.g., 200 Å versus 100 Å).

The organic stack of Device Examples 17-20 consisted of sequentially, from the ITO surface, 100 Å of P1 as the hole injection layer (HIL), 300 Å of NPD as the hole transport layer (HTL), 300 Å of the invention compound doped with 10 wt % or 15 wt % of P1, an Ir phosphorescent compound, as the emissive layer (EML), 50 Å or 100 Å of HPT or the invention compound as enhancement layer (ETL2), an electron transport layer (ETL1) of Alq₃ having a thickness identified in Table 5, and a LiF/Al cathode. In particular, the BL and ETL have a sum total of 500 Å. Thus, the general device structure for the devices of Table 5 was: ITO(1200 Å)/P1 (100 Å)/NPD(300 Å)/Host: P1 x % (300 Å)/ETL2 (50 Å or 100 Å)/Alq3 (400 Å or 450 Å)/LiF(10 Å)/Al(1000 Å).

TABLE 6 At 1000 cd/m² At 40 mA/cm² Device Host Dopant ETL2 ETL1 CIE V L.E. EQE PE L₀ LT_(80%) example Cmpd x % (Å) (Å) X Y (V) (cd/A) (%) (lm/W) (cd/m²) (hr) 17 23 P1 10% 23 Alq₃ 0.355 0.605 7.1 42.2 11.7 18.66 13,580 160 (100 Å) (400 Å) 18 23 P1 15% 23 Alq₃ 0.353 0.609 6.8 42.1 11.6 19.44 14,521 155 (100 Å) (450 Å) 19 23 P1 1% HPT Alq₃ 0.355 0.607 6.8 46.9 13 21.66 14,728 94 (50 Å) (450 Å) 20 23 P1 15% HPT Alq₃ 0.352 0.611 6.6 44.9 12.3 21.36 15,070 63 (50 Å) (400 Å)

The data in Table 6 describes the performance of Devices Examples 17-20. The voltage, luminous efficiency, external quantum efficiency and power efficiency data were measured at 1000 cd/m² (display level brightness). The lifetime was measured at accelerated conditions: 40 ma/cm² DC. The initial device luminance (L₀) at life-test conditions (40 mA/cm²) is also shown in Table 5. Compound 23 was used as a host for the green phosphorescent emitter P1. Two different dopant concentrations (10% or 15%) and two different ETL1 layers (Alq₃ of 400 Å or 450 Å) were varied in the devices and tested experimentally. The data show no significant difference in the device performance due to dopant concentration variation. However, there was a difference in the device performance due to variation in the ETL1 layer. In devices having HPT as the ETL1 layer, the device efficiency was slightly higher due to stronger BL properties of HPT. However, the lifetime of the devices with Compound 23 as the ETL1 was longer. The data suggests that Compound 23 can be used as an efficient host for green phosphorescent emitter and as a ETL1 in the device. The stability of devices having Compound 23 as the ETL1 layer in the devices is higher than the stability of devices having a similar overall structure except with HPT as the ETL1 layer.

The organic stack of Device Examples 21-24 consisted of sequentially, from the anode surface, 100 Å of P1 or LG101 as the hole injection layer (HIL), 300 Å of NPD as the hole transport layer (HTL) or no HTL, 300 Å of the invention compound doped with 9 wt %, 15 wt % or 20 wt % of P2 or P7 Ir phosphorescent compounds as the emissive layer (EML), 50 Å, 150 Å or 250 Å of H1 as the enhancement layer (ETL2), and 200 Å, 300 Å or 400 Å of Alq₃ as the electron transport layer (ETL1). The materials and thicknesses of Device Examples 21-24 are provided in Table 7. The devices were tested, and the corresponding results measured are provided in Table 8.

TABLE 7 Device Anode HIL HTL EML ETL2 ETL1 21 ITO LG101 none H1: P2 15% [600 Å] H1 [250 Å] Alq₃ [800 Å] [100 Å] [200 Å] 22 ITO LG101 NPD H1: P2 9% [300 Å] H1 [50 Å] Alq₃ [2000 Å] [100 Å] [300 Å] [400 Å] 23 ITO P1[100 Å] NPD H1: P7 9% [300 Å] H1 [50 Å] Alq₃ [800 Å] [300 Å] [400 Å] 24 Sapphire/IZO LG101 none H1: P7 20% [300 Å] H1 [150 Å] Alq₃ [800 Å] [100 Å] [300 Å]

TABLE 8 At L₀ = At 1000 cd/m² At 10 1000 V LE EQE PE mA/cm² cd/m² Device (V) (cd/A) (%) (lm/W) CIE x CIE y LT_(80%) (hr) 21 12.9 10.0 5.3 2.4 0.160 0.285 352 22 7.6 10.9 6.6 4.5 0.155 0.234 77 23 9.0 12.1 6.0 4.2 0.162 0.317 151 24 7.1 8.9 5.5 4.0 0.145 0.232 205

From Devices 21, 22, 23, and 24 it can be seen that the devices demonstrate differences between device structures having an emissive layer containing H1 and an emissive compound P2 or P7. Device Example 21 did not have an HTL, and used a thick EML to enhance device operational stability. The measured CIE coordinates of Device Example 21 were not blue saturated, so the structures of Device Examples 22, 23, and 24 used a 30 nm EML. Device Example 22 also incorporated a 200 nm ITO layer to saturate the device blue CIE. Device Example 23 was a standard blue PHOLED that was not optimized for operational stability. Device Example 24 was a blue PHOLED using the same emissive compound P7 as used in Device Example 23. However, Device Example 24 had several features that enabled longevity such as no NPD, sapphire heat sink substrate, a thick blocking layer, and high emitter concentration. Hence, the LT_(80%) of Device Example 24 exceeded the LT_(80%) of Device Example 23, and Device Example 24 had improved blue CIE compared to Device Example 23.

FIG. 3 shows an organic light emitting device having only a layer with a high hole conductivity between an emissive layer and the anode, an enhancement layer of the same material used as a non-emissive host in the emissive layer, and an emissive layer having first and second organic layers with different concentrations of phosphorescent material and non-emissive materials, where the concentration of phosphorescent material in the second organic layer is variable. The device of FIG. 3 includes a 10 nm thick hole injection layer of LG101, a 30 nm thick first organic emissive layer of H1 doped with 30 wt % P2, a 30 nm thick second organic emissive layer of H1 doped with X wt % P2, a 25 nm thick enhancement layer of H1, a 20 nm thick electron transport layer of Alq₃, and a LiF/Al cathode. X varies from 10 wt % to 18 wt % in the devices fabricated, with devices at X=10, 14 and 18 wt % as indicated in the legends for FIG. 4.

FIG. 4 shows a plot of normalized luminescence versus time for the device of FIG. 3.

FIG. 5 shows a plot of external quantum efficiency versus luminance for the device of FIG. 3.

FIG. 6 shows a plot of power efficacy versus luminance for the device of FIG. 3.

FIG. 7 shows a plot of luminance versus voltage for the device of FIG. 3.

FIG. 8 shows a plot of EL intensity versus wavelength for the device of FIG. 3.

FIG. 9 shows an organic light emitting device having only a layer with a high hole conductivity between an emissive layer and the anode, an enhancement layer of the same material used as a non-emissive host in the emissive layer, and an emissive layer having first and second organic layers with different phosphorescent materials in the first and second organic layers, where the concentration of phosphorescent material in the second organic emissive layer is variable. The device of FIG. 9 includes a 10 nm thick hole injection layer of LG101, a 30 nm thick first organic emissive layer of H1 doped with 30 wt % P1, a 30 nm thick second organic emissive layer of H1 doped with X wt % P2, a 25 nm thick enhancement layer of H1, a 20 nm thick electron transport layer of Alq₃, and a LiF/Al cathode. X varies from 10 wt % to 18 wt % in the devices fabricated, with devices at X=10, 14 and 18 wt % as indicated in the legends for FIG. 4. The device of FIG. 9 is very similar to that of FIG. 3, with the difference being that the device of FIG. 9 uses different emissive phosphorescent material in the first and second organic emissive layers, while the device of FIG. 3 uses the same phosphorescent material in both layers. The concentrations of the phosphorescent materials are the same in the device of FIG. 3 compared to the device of FIG. 9.

FIG. 10 shows a plot of external quantum efficiency versus luminance for the device of FIG. 9.

FIG. 11 shows a plot of power efficacy versus luminance for the device of FIG. 9.

FIG. 12 shows a plot of luminance versus voltage for the device of FIG. 9.

FIG. 13 shows a plot of EL intensity versus wavelength for the device of FIG. 9.

The device of FIG. 9 may be compared to the device of FIG. 3. In terms of device architecture, the devices are similar except in the emissive layer, where the device of FIG. 9 has an emissive layer doped with phosphorescent emitter P1 and another emissive layer doped phosphorescent emitter P2, whereas the device of FIG. 3 has only phosphorescent emitter P2. Both devices have a step in dopant concentration, and similar concentrations even in the layers where the actual dopant is different. Several points can be understood from comparing these two device architectures. First, the device of FIG. 9 exhibits a broad emission spectra that is a combination of emission from both P1 and P2. As a result, it can be inferred that the device of FIG. 3 is emitting from both the layer doped with 30% P2 and the layer doped with a lesser concentration of P2. Comparing FIG. 5 to FIG. 10, it can be seen that the device of FIG. 9 has better charge balance than the device of FIG. 3, as evidenced by a relatively flat external quantum efficiency over three orders of magnitude for the device of FIG. 9 as compared to two orders of magnitude for the device of FIG. 3.

It is understood that the various embodiments described herein are by way of example only, and are not intended to limit the scope of the invention. For example, many of the materials and structures described herein may be substituted with other materials and structures without deviating from the spirit of the invention. The present invention as claimed may therefore includes variations from the particular examples and preferred embodiments described herein, as will be apparent to one of skill in the art. It is understood that various theories as to why the invention works are not intended to be limiting. 

1. A compound selected from the group consisting of:

wherein each of R₁ through R₈ are independently selected from the group consisting of any alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, heteroaryl and hydrogen, and where each of R₁ through R₈ may represent multiple substitutions.
 2. The compound of claim 1, wherein the compound is selected from the group consisting of:


3. The compound of claim 1, wherein the compound is:

wherein each of R₁ through R₈ is are independently selected from the group consisting of any alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, heteroaryl and hydrogen, and where each of R₁ through R₈ may represent multiple substitutions.
 4. The compound of claim 3, wherein the compound is:


5. An organic light emitting device comprising: an anode; a cathode; and an organic layer, disposed between the anode and the cathode, the organic layer further comprising a compound selected from the group consisting of:

wherein each of R₁ through R₈ are independently selected from the group consisting of any alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, heteroaryl and hydrogen, and where each of R₁ through R₈ may represent multiple substitutions.
 6. A consumer product comprising a device, the device further comprising: an anode; a cathode; and an organic layer, disposed between the anode and the cathode, the organic layer further comprising a compound selected from the group consisting of:

wherein each of R₁ through R₈ are independently selected from the group consisting of any alkyl, alkoxy, amino, alkenyl, allcynyl, arylkyl, aryl, heteroaryl and hydrogen, and where each of R₁ through R₈ may represent multiple substitutions.
 7. The compound of claim 1, wherein the compound is:

wherein each of R₁ through R₈ are independently selected from the group consisting of any alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, heteroaryl and hydrogen, and where each of R₁ through R₈ may represent multiple substitutions.
 8. The compound of claim 7, wherein the compound is:


9. The compound of claim 1, wherein the compound is:

wherein each of R₁ through R₈ are independently selected from the group consisting of any alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, heteroaryl and hydrogen, and where each of R₁ through R₈ may represent multiple substitutions.
 10. The compound of claim 9, wherein the compound is:


11. The compound of claim 1, wherein the compound is:

wherein each of R₁ through R_(s) are independently selected from the group consisting of any alkyl, alkoxy, amino, alkenyl, alkynyl, arylkyl, aryl, heteroaryl and hydrogen, and where each of R₁ through R₈ may represent multiple substitutions.
 12. The compound of claim 11, wherein the compound is: 